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Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center for Space Physics, Boston University Dynamical Processes in Space Plasmas Israel, 10-17 April 2010

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Page 1: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High-

Latitude E-Region Electrojet

Y. Dimant and M. Oppenheim

Tuesday, April 13, 2010

Center for Space Physics, Boston University

Dynamical Processes in Space Plasmas Israel, 10-17 April 2010

Page 2: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Outline

• Background and motivation• Anomalous electron heating• Nonlinear current; energy deposition• 3-D and 2-D fully kinetic modeling of E-region

instabilities• Anomalous conductivity• Conclusions; future work

Page 3: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Solar CoronaSolar Corona Solar WindSolar WindIonosphereIonosphereMagnetosphereMagnetosphere

Inner Boundary for Solar-Terrestrial System

Page 4: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Earth’s Ionosphere

Page 5: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

What’s going on?

• Field-aligned (Birkeland) currents along equipotential magnetic field lines flow in and out.

• Mapped DC electric fields drive high-latitude electrojet (where Birkeland currents are closed).

• Strong fields also drive E-region instabilities: turbulent field coupled to density irregularities.– Turbulent fields give rise to anomalous heating.– Density irregularities create nonlinear currents.

• These processes can affect macroscopic ionospheric conductances important for Magnetosphere-Ionosphere current system.

Page 6: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Motivation

• How magnetospheric energy gets deposited in the lower ionosphere?

• Global magnetospheric MHD codes with normal conductances often overestimate the cross-polar cap potential (about a factor of two).

• Anomalous conductance due to E-region turbulence can account for discrepancy!

Page 7: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Strong electron heating

Reproduced from Foster and Erickson, 2000125 mV/m

Page 8: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

(Reproduced from Stauning & Olesen, 1989)

Page 9: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Anomalous Electron Heating (AEH)

• Anomalous heating: Normal ohmic heating by E0 cannot account in full measure.

• Farley-Buneman, etc. instabilities generate E.

• Heating by major turbulent-field components E B is not sufficient.

• Small E|| || k|| || B, |E|||<<|E|, are crucial:

– Confirmed by recent 3-D PIC simulations.

Page 10: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Analyitical Model of AEH• Dimant & Milikh, 2003:

– Heuristic model of saturated FB turbulence (HMT),– Kinetic simulations of electron distribution function.

• Difficult to validate HMT by observations:– Radars:

• Pro: Can measure k|| (aspect angle ~ 1o),• Con: Only one given wavelength along radar LOS.

– Rockets: • Pro: Can measure full spectrum of density irregularities

and fields,• Con: Hard to measure E||; other diagnostic problems.

• Need advanced and trustworthy 3-D simulations!

Page 11: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center
Page 12: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

PIC simulations: electron density

E0 x B direction

E0 d

irec

tion

Page 13: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

3D simulations3D simulations• 256x256x512 Grid256x256x512 Grid

• Lower Altitude (more collisional)Lower Altitude (more collisional)

• Driving Field: ~4x Threshold field (150 Driving Field: ~4x Threshold field (150 mV/m at high latitudes)mV/m at high latitudes)

• Artificial eArtificial e-- mass: m mass: me:sime:sim = 44m = 44mee; ;

ExB direction (m)ExB direction (m)

E0

dir

ecti

on

(m

) B0

dir

ecti

on

(m

)

00

102

102

1020

0

410

Potential (x-y cross-section)

Potential (x-z cross-section)

4 Billion 4 Billion virtual PIC virtual PIC particlesparticles

2D looks the 2D looks the same!same!

Page 14: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Higher altitude 3D simulationHigher altitude 3D simulationIons: First Moment (RMS Of Vi)electrons: First Moment (RMS Of Ve)

3-D

Tem

ps

3-D

Tem

ps

2-D

Tem

ps

2-D

Tem

ps

Page 15: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

100 105 110 115 120 125 130 135h,km

500

1000

1500

2000

2500

3000

3500radareffT

Anomalous heating

eT

iT

0T

[Milikh and Dimant, 2003] E = 82 mV/m

(comparison with Stauning and Olesen [1989])

Page 16: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Cross-polar cap potential

(Merkin et al. 2005)

Page 17: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Anomalous Electron Heating (AEH)

• Affects conductance indirectly:– Reduces recombination rate,– Increases density.

• All conductivities change in proportion.• Inertia due to slow recombination changes:

– Smoothes and reduces fast variations.

• Can account only for a fraction of discrepancy.• Need something else, but what?

Page 18: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Nonlinear current (NC)

• Direct effect of plasma turbulence:– Caused by density irregularities, n.

• Only needs developed plasma turbulence – no inertia and time delays.

• Increases Pedersen conductivity (|| E0)– Crucial for MI coupling!

• Responsible for the total energy input, including AEH.

Page 19: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Characteristics of E-region waves• Electrostatic waves nearly perpendicular to

• Low-frequency,

• E-region ionosphere (90-130km): dominant collisions with neutrals

- Magnetized electrons:

- Demagnetized ions:

• Driven by strong DC electric field,

• Damped by collisional diffusion (ion Landau damping for FB)

0 ||, k kB

ene

ini

0 0E B

en

Page 20: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

0B

0E

20000 / BBEV

electronsions

Two-stream conditions

(magnetized electrons + unmagnetized ions)

Page 21: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Wave frame of reference

0E

_+_

+_ __

++ + +

_ _ _

+

+ + +

+

__ _ _

E E

0n

20000 BBEV

Ions

0n

0n

0n

Phn VV

Electrons

0B

Page 22: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

00 BE

0E

E

E

-e

-eNLJ

Nonlinear Current

Page 23: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Mean Turbulent Energy Deposit

• Work by E0 on the total nonlinear current• Buchert et al. (2006):

– Essentially 2-D treatment,– Simplified plasma and turbulence model.

• Confirmed from first principles.• Calculated NC and partial heating sources:

– Full 3-D turbulence,– Arbitrary particle magnetization,– Quasi-linear approximation using HMT.

Page 24: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Anomalous energy deposition

jEjEjE jEjE

NC000 jEjEjE

Nonlinear current:

Vnqj

NC

jEjE

0

NC0 jE is total energy source for turbulence!

How 2-D field and NC can provide 3-D heating?

Density fluctuations in 3-D are larger than in 2-D!

Page 25: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

3-D vs. 2-D, Densities

Page 26: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Nonlinear current (NC)

• Mainly, Pedersen current (in E0 direction).

• May exceed normal Pedersen current.

• May reduce the cross-polar cap potential.

• Along with the anomalous-heating effect, should be added to conductances used in global MHD codes for Space Weather modeling

Page 27: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

E-region turbulence and Magnetosphere-Ionosphere Coupling

• Anomalous electron heating, via temperature-dependent recombination, increases electron density.

• Increased electron density increases E-region conductivities.

• Nonlinear current directly increases mainly Pedersen conductivity.

• Both effects increase conductance and should lower cross polar cap potentials during magnetic storms.

• Could be incorporated into global MIT models.

Page 28: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Conclusions

• Theory & PIC simulations: E-region turbulence affects magnetosphere-ionosphere coupling:– (1) Anomalous electron heating, via temperature-dependent

recombination, increases electron density.• Increased electron density increases E-region conductivities.

– (2) Nonlinear current directly increases electrojet Pedersen conductivity.

• Responsible for total energy input to turbulence.

– Both anomalous effects increase conductance and should lower cross-polar cap potentials during magnetic storms.

• Will be incorporated into a global MHD model.

Page 29: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Fully Kinetic 2-D SimulationsSimulations Parameters:• Altitude ~101km in Auroral region• Driving Field: ~1.5 Threshold field (50 mV/m at high

latitudes)• Artificial e- mass: me:sim = 44me; mi:sim=mi

• 2-D Grid: 4024 cells of 0.04m by 4024 cells of 0.04m• Perpendicular to geomagnetic field, B• 8 Billion virtual PIC particles• Timestep: dt = s (< cyclotron and plasma frequencies)

E2 (

V/m

)2

Time (s)

ExB direction (m) ExB direction (m)

E0 d

irec

tio

n (

m)

Page 30: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

Threshold electric field

FB: Farley-Buneman instability

IT: Ion thermal instability

ET: Electron thermal instability

CI: Combined (FB + IT + ET) instability

1: Ion magnetization boundary

2: Combined instability boundary

High-latitude ionosphereEquatorial ionosphere

[Dimant & Oppenheim, 2004]

Page 31: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

3-D vs. 2-D, Temperatures

• 3-D Simulations get hotter!3-D Simulations get hotter!

Electron Moments <Vx,y,z2> Ion Moments <Vx,y,z

2>

T$mp$ratur$s 0:

0.0 0.1 0.2 0.3tim$ (s)

400

600

800

1000

T (

K)

x0 y0 z0

FBI 128x128 psi=.3 M$=88m$ dx=0.08 E=140mV W$d May 17 15:43:21 2006

T$mp$ratur$s 1:

0.0 0.1 0.2 0.3tim$ (s)

300350

400

450

500

550

600

T (

K)

x1

y1

z1

FBI 128x128 psi=.3 M$=88m$ dx=0.08 E=140mV W$d May 17 15:43:21 2006

V$lociti$s 0:

0.0 0.1 0.2 0.3tim$ (s)

-1000

0

1000

2000

3000

V (

m/s

)

Vx0

Vy0 Vz0

V_hall0

V_p$d0

FBI 128x128 psi=.3 M$=88m$ dx=0.08 E=140mV W$d May 17 15:43:21 2006

V$lociti$s 1:

0.0 0.1 0.2 0.3tim$ (s)

0

50

100

150

200

V (

m/s

)

Vx1

Vy1

Vz1

V_hall1

V_p$d1

FBI 128x128 psi=.3 M$=88m$ dx=0.08 E=140mV W$d May 17 15:43:21 2006

3-D

Tem

p2-

D T

emp

Time (s) Time (s)

Page 32: Magnetosphere-Ionosphere Coupling through Plasma Turbulence at High- Latitude E-Region Electrojet Y. Dimant and M. Oppenheim Tuesday, April 13, 2010 Center

‘5-moment’ transport equations

0

Ch

2 / 32 / 3

1. Continuity equation :

0, (quasineutrality: )

2. Momentum equation (in neutral frame of reference) :

3. Thermal balance equation :

e i

n

nn n n

t

n Tdm q m

dt n

d Tn

dt n

V

VE V B V

ange of enthropy Frictional heatingCollisional cooling

22,

3

where: / , is fraction of collisional energy loss

n n n n

n n n

dV T T

dt t

m m m m

V

Fluid-model equations for long-wavelength waves: they do not include heat conductivity, Landau damping, etc., but contain all essential factors.